Hey filipu - Ride sounds like a fun one!
On my Inner Mongocan ride last August I went out via Chengde and back thru Zhangjiakou.
I see you're heading out of Beijing straight NORTH, but if you choose one of the above areas for your ride back, send me a shout and I can dig up the coordinates:

Beijing-Chengde
Some cool farm roads and S-Roads outside of Zhangjiakou heading back towards Beijing's Baihepu and Dishuihu

Zhangjiakou-Beijing
Cool roads "around Bolitai" (Although the actual road up Bolitai itself isn't much fun: corners too tight to be considered fun twisties, but roads around there are nice!)

For Inner Mongolia, the best of the desert landscape I encountered was north of Sonid Youqi (click for map).
For photos, see this RR Post: Xinlin Gol to Sonid Youqi